1. Field of the Invention
The present invention relates to an actuator and, more particularly, to an actuator for precise and high-speed movement, which is suitably applicable to the seeking system for the recording/reproducing head of an opto-magnetic recording apparatus, a hard disc drive apparatus, etc.
2. Related Art
One prior art actuator of a voice-coil type is shown in FIG. 12, which essentially comprises a yoke 1 formed in a shape of rectangular frame, a permanent magnet 2 mounted to the inner wall of one side 1a of the yoke 1 and a moving coil 3 wound around the opposite side 1b of the yoke 1. Magnetic flux generated from the permanent magnet 2 enters in the side 1b to form a magnetic field within the space between the permanent magnet 2 and the side 1b of the Yoke 1. When the coil 3 is supplied with energizing current, it moves along the side 1b due to the electromagnetic force by the magnetic field. In this case, the moving direction of the coil 3 is determined by the flowing direction of the energizing current.
However, in the actuator of such structure, since the coil 3 exists between the permanent magnet 2 and the side 1b of the Yoke 1, a considerably large gap must be formed between them, which lowers the operating point of the permanent magnet 2. In other words, the flux density generated from the permanent magnet 2 becomes small for the energy product of the permanent magnet 2, so that the efficiency of the actuator is lowered. For that, it has been adopted a method of flowing a large current in the coil 3 in order to obtain a driving force having a desired magnitude. However, this method has disadvantages that the large energizing current often the generation of a large amount of heat by the Joule effect, which, in turn, causes differences in thermal expansion among respective parts in the apparatus. As a result, the read-out of the recorded data is impossible in some cases.